WO2008072368A1

WO2008072368A1 - Glass polarizer for visible light

Info

Publication number: WO2008072368A1
Application number: PCT/JP2007/001366
Authority: WO
Inventors: Khaled Jabri; Atsushi Arai; Hiromichi Nishimura; Yoshihiko Noro; Dai Takeda
Original assignee: Okamoto Glass Co., Ltd.
Priority date: 2006-12-15
Filing date: 2007-12-06
Publication date: 2008-06-19
Also published as: ES2404064T3; EP2093595B1; EP2093595A1; CN101427165A; JP4928564B2; CN101427165B; JPWO2008072368A1; HK1132333A1; EP2093595A4; US8077389B2; US20090168172A1

Abstract

This invention provides a glass polarizer which can be applied, for example, to projection-type liquid crystal display devices, is produced using a silver halide-containing glass as a starting material, and has excellent transmittance and extinction ratio to light having a visible light range (500 nm to 600 nm). The glass polarizer for visible light is a polarizer produced by heat treating a borosilicate glass to dispersion precipitate silver halide particles, heat stretching the borosilicate glass, and then reducing at least a part of the silver halide particles aligned and elongated in the glass to metallic silver particles. The glass polarizer for visible light is characterized in that the average transmittance (T⊥% 500 to 600 nm) of a wavelength range of 500 nm to 600 nm in light having a polarization plane orthogonal to the longitudinal direction of the metallic silver particles with a shape anisotropy, which have been uniaxially aligned and dispersed, is not less than 75%, and the extinction ratio in the above wavelength range is not less than 25 dB.

Description

Specification

Visible glass polarizer

Technical field

[0001] The present invention relates to a glass polarizer having polarization characteristics that can be industrially used for light in the visible light region. In particular, the present invention relates to a glass polarizer for visible light having excellent heat resistance and light resistance that can be used as a polarizer for a projection type liquid crystal display device.

Background art

In recent years, projection liquid crystal display devices have been widely used as video display devices that display large screens. The rear projection type liquid crystal display device is mainly used for presentation of personal computer data, and the front projection type liquid crystal display device is mainly used for presentation of personal computer data. The projection type liquid crystal display device has a configuration in which an image on a small liquid crystal element is enlarged and projected on a large screen using a projection optical system. A technically detailed description can be found, for example, in Non-Patent Document 1 (large screen display).

FIG. 1 shows a configuration diagram of a typical projection type liquid crystal display device. The light from the light source 4 is separated into blue (B), green (G) and red (R) components by optical components 5 to 16, and the liquid crystal elements 2 B, 2 G and 2 R corresponding to the respective components. Led to. Each liquid crystal display element 2R, 2G and 2B has an incident side polarizer 1R, 1G and 1B on the incident side and an output side polarizer 3R, 3G and 3B on the output side. . A pair of polarizers composed of an entrance-side polarizer and an exit-side polarizer, corresponding to red, green, and blue, has a function of selectively passing light having a predetermined polarization direction that has passed through the liquid crystal element. With this function, the light of the three primary colors that has passed through the liquid crystal elements 2R, 2G, and 2B becomes a light intensity modulated image signal. These three primary colors are further synthesized by a synthesis prism 17 and further projected onto a screen 19 through an enlarged projection lens system 18.

[0004] The polarization characteristic required for the polarizing element is to transmit an optical signal having a desired polarization plane and to block an unnecessary optical signal having a polarization plane orthogonal to the optical signal. In other words, it is desirable to have a large transmittance for light having a desired polarization plane and a small transmittance for light having a polarization plane orthogonal to the light.

[0005] The ratio of these transmittances is called an extinction ratio, and is widely used by those skilled in the art as a figure of merit that expresses the performance of a polarizing element. If this index is used, the performance required for a polarizing element applied to a projection type liquid crystal display device is expressed as having a large transmittance and a large extinction ratio for an optical signal. It is said that an industrially available polarizer preferably has a transmittance of 70 <½ or more with respect to light of a wavelength to be used and an extinction ratio of 10: 1, preferably 30: 00: 1. (Patent Document 1)

[0006] A social demand for a projection-type liquid crystal display device is to realize a larger and clearer image with a smaller device. To meet this demand, the application of a light source with a larger amount of light and the use of a liquid crystal element with a smaller area are recent technological trends. As a result, high energy density light is introduced not only into the liquid crystal element but also into the polarizer placed before and after the liquid crystal element. A polarizer having a function of absorbing unnecessary light is required to have particularly high heat resistance and light resistance.

[0007] According to the principle of polarizers, there are dichroic polarizers and non-dichroic polarizers (such as Brewster polarizers) that selectively absorb light depending on the plane of polarization (Patent Document 2). See). The dichroic polarizer is a desirable element for a projection type liquid crystal display device that is particularly required to be miniaturized because the element is thin and does not require a special device that absorbs unnecessary light.

[0008] Currently, the only dichroic polarizing element that achieves practical optical performance in the visible light region is a polarizing film made of an organic material. However, a polarizer made of an organic resin has a decisive drawback of low heat resistance (see Patent Document 1).

In order to eliminate this drawback, a polarizing film made of an organic resin is used by being bonded to a sapphire substrate having high thermal conductivity (Patent Document 3). However, polarizers bonded with sapphire with excellent thermal conductivity are also in line with technical demands for higher brightness in recent years. In other words, light absorption by the polarizing element in the green region where the brightness is the highest ■ Projection-type liquid crystal display to protect the organic resin film from heat without satisfying the requirement that the polarizer function does not deteriorate due to heat generation The equipment is equipped with a cooling device including a cooling fan. Cooling devices not only contradict the social need for miniaturization, but also create another problem of noise.

[0010] As a method for solving this technical problem, an idea of applying polarized glass applied to an element for optical communication has been proposed (Patent Document 1). However, the optical wavelength used for optical communication is in the far-infrared region and is significantly different from visible light. Therefore, the technology of glass polarizer for optical communication immediately controls the light of the projection type liquid crystal display device. Is not immediately applicable. The invention disclosed in Patent Document 1 does not disclose a technique for imparting an effective characteristic to light in the visible light region to a glass polarizing element. It is difficult to realize a projection type liquid crystal display device using a child.

[001 1] Here, the technical background of polarizing glass will be briefly described. Polarized glass is characterized in that it contains fine metal particles with shape anisotropy oriented and dispersed in an optically transparent glass substrate, and is an anisotropic surface plasmon present on the surface of fine metal particles. The polarization characteristic is realized by using a unique resonance absorption phenomenon (see Patent Document 4 and Non-Patent Document 2).

[0012] FIG. 2 shows the surface plasmon resonance absorption characteristics of the metal fine particles cited from Patent Document 4. Graph A in Fig. 2 corresponds to surface plasmon resonance absorption by spherical metal particles. On the other hand, the resonance absorption of rod-shaped metal particles having shape anisotropy exhibits different characteristics depending on the correlation between the polarization plane of incident light and metal particles having shape anisotropy.

[0013] When the polarization plane is parallel to the longitudinal direction of the metal fine particles, the characteristics indicated by B are exhibited. Compared to characteristic A, it can be seen that the wavelength of resonance absorption has shifted to a longer wavelength. It is known that this resonance absorption wavelength depends on the ratio of the major axis to the minor axis of the metal fine particles, and that the greater the ratio, the greater the resonance absorption wavelength (see Non-Patent Document 2). On the other hand, for light having a polarization plane perpendicular to the longitudinal direction, the property expressed by property C is exhibited. [0014] From FIG. 2, it is understood that this glass exhibits polarization characteristics with respect to light in the vicinity of 60 nm. That is, light having a polarization plane parallel to the longitudinal direction of the metal particles has a small transmittance due to strong absorption. The transmittance for light having a polarization plane parallel to the longitudinal direction of the metal particles is expressed as T || <½. On the other hand, the light having a polarization plane perpendicular to the longitudinal direction of the metal particles has a small absorption, and therefore shows a higher transmittance. The transmittance for light having a polarization plane perpendicular to the longitudinal direction of the metal particles is expressed as just%. With this mechanism, polarization characteristics are realized. The characteristics disclosed in FIG. 2 are the characteristics required for the projection type liquid crystal display device, that is, the ratio between the parallel absorption curve Β and the vertical absorption curve C between 500 nm and 600 nm, In other words, it has not realized that the extinction ratio is sufficiently large and that the parallel absorptivity value is sufficiently large.

[0015] Many techniques have been proposed for polarizing glass and glass polarizers using polarizing glass. Many of these technologies relate to glass polarizers that can be applied to light in the infrared region (Patent Documents 5 and 6, etc.), and are used for the projection type liquid crystal display device that is the object of the present invention. A technique applicable to light in the visible light region is not disclosed.

There are few inventions related to glass polarizers that can be applied to light in the visible light region. Patent Document 7 is a technology that provides a polarizing element effective for light in the visible light region by utilizing the characteristics of copper fine particles having shape anisotropy (the disclosed characteristics are applied to FIG. 3). As shown in Fig. 3, it is not possible to achieve a large extinction ratio, especially for wavelengths below 600 nm, ie parallel transmission with respect to the transmission curves C and E perpendicular to the stretching axis. It is concluded that there is no practical characteristic that the ratio (extinction ratio) of the D and F values of the rate curves is small and the transmittance C is only 10 to 60%. The

[0017] Patent Document 8 discloses a technique that realizes dichroic absorption with respect to wavelengths in the visible light region. The characteristics applicable to the projection type liquid crystal display device to which the present invention is intended, that is, Since there is no specific and quantitative description of achieving high transmittance and high extinction ratio, it cannot be realized as a polarizer. Similarly to Patent Document 8, Patent Document 9 proposes a technique for obtaining an effective extinction ratio in the visible light region, and does not disclose a technique for realizing high transmittance.

[0018] CODIXX is a manufacturing technology that introduces silver ions by diffusing from the glass surface, deposits silver fine particles by heat treatment, and then stretches them to impart shape anisotropy to the silver fine particles. Is used to sell polarizing glass that is effective in the visible light region (Non-patent Document 3). However, the ion diffusion process is generally unstable, and the concentration distribution of silver ions in the glass thickness direction tends to cause nonuniformity in the size of the silver particles produced. As a result, there is a weak point that the characteristic variation of the polarizer occurs. Furthermore, since the stretching particles are solid metallic silver particles, they cannot be stretched unless the stretching tension is larger than the silver halide grains that are stretched in a droplet state, so that there is a problem that the glass tends to break during stretching. .

[0019] A communication infrared light glass polarizer widely used in industry uses a different manufacturing method. That is, as disclosed in Patent Document 4 and Patent Document 5, a production method is adopted in which silver fine particles are produced by once precipitating silver halide and then reducing the silver halide. However, a polarizer produced by this production method does not exhibit practical performance that can be used in the visible range (Patent Document 5). For example, FIG. 1 of Patent Document 5 (cited as FIG. 4 in this specification) and paragraph “0 0 2 2” of the specification state as follows. “■ · Silver halide glass is unsatisfactory to produce an effective optical polarizer over the entire range of 4 0 0 η Γη _ 7 0 0 nm.”

[0020] As described above, there is no glass polarizer for visible light applicable to a projection type liquid crystal display device based on a stable manufacturing technique widely applicable industrially.

[0021] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-7 7 8 50

Patent Document 2: Special Table 2 0 0 2— 5 1 9 7 4 3

Patent Document 3: Japanese Patent Application Laid-Open No. 2 0 00 _ 2 0 6 5 0 7 Patent Document 4: U.S. Pat.No. 4,479,8 1 9

Patent Document 5: Japanese Patent No. 1 6 1 8477

Patent Document 6: Japanese Patent No. 274060 1

Patent Document 7: Japanese Patent No. 2885655

Patent Document 8: Special Table 2004-523804

Patent Document 9: Japanese Patent Publication No. 2-406 19

Patent Document 10: Japanese Patent No. 26280 14

Patent Document 11: Japanese Patent No. 3549 1 98

Non-Patent Literature 1: Nobuo Nishida, Large Screen Display (Series Advanced Display Technology 7), Kyoritsu Publishing, Tokyo, 2002

Non-Patent Document 2: S. L ink and M. A. E I _S ay ed, J. P h y s. Ch em. B 1 03 (1 999) 84 1 0-8426

Non-Patent Literature 3: Takuichi Suzuki, Industrial Materials Vol.52, No.12, pp. 102-107

Disclosure of the invention

Problems to be solved by the invention

[0022] The present invention is applicable to a projection-type liquid crystal display device, etc., starting from silver halide-containing glass, and has excellent transmittance and quenching for light in the visible light region (500 nm to 600 nm). It is an object to provide a technique for realizing a glass polarizer having a ratio.

Means for solving the problem

The glass polarizing element of the present invention utilizes surface plasmon resonance of metal fine particles having shape anisotropy oriented and dispersed in glass. While using the same principle, the prior art shown in Fig. 4 has not realized the performance that a polarizer applicable to a projection-type liquid crystal display device should have. The reason for this will be described with reference to FIG.

[0024] Curve C in Fig. 2 shows that surface plasmon resonance absorption for light having a polarization plane orthogonal to the longitudinal direction of the metal fine particles having shape anisotropy exists around 380 nm. At the same time, curve C in Figure 2 shows that the effect extends from 500 nm to 600 nm. This effect is the polarization plane to pass It shows that it has the effect of transmitting light having a higher transmittance. At the same time, the curve B shows the absorption of light with a polarization plane parallel to the longitudinal direction, which indicates that the difference in polarization plane causes a large difference in the absorptivity, that is, the transmittance near 600 nm.

[0025] In the case of a polarizer applied to light in the infrared region, since the transmitted light is far away from the wavelength of this resonance absorption, the above effect is negligible and does not cause a practical problem. On the other hand, in the case of realizing a polarizing element for visible light, the above effect is at a level that cannot be ignored. Therefore, in order to realize a glass polarizer applied to the green region visible light, a new technical means for minimizing the light absorption in the wavelength region of 500 nm to 600 nm is required. As a simple technical measure, it is possible to suppress this absorption by reducing the concentration of metal particles and improve the transmittance for transmitted light. However, if such a technical measure is adopted, it should be suppressed. It becomes difficult to suppress light having a polarization plane. As a result, the necessary extinction ratio cannot be realized.

[0026] As a result of studying this problem, the inventors have found that the transmittance in the vicinity of 500 nm can be improved by reducing the size of the silver particles. That is, by using silver particles prepared from silver halide having a particle size of 40 nm or less, the transmittance T 丄% for light having a polarization plane perpendicular to the longitudinal direction of the metal fine particles is increased. Found that it would be possible.

[0027] Furthermore, the use of silver halide having a small particle size is achieved by the transmittance T II of light blocked by a polarizer, that is, light having a polarization plane parallel to the longitudinal direction of metal fine particles having shape anisotropy. It produced another effect of suppressing 0/0 to a small value close to 500 nm. As a result, by using silver halide with a small grain size, it is possible not only to increase the transmittance of light to be transmitted, but also to increase the extinction ratio. It became possible to keep.

[0028] The present invention is based on the conventional technology in that the starting material is a glass material in which silver halide is dispersed and precipitated. In order to realize an effective function for light in the visible light region, Need to add technology. [0029] The conventional polarizing glass technology using silver halide for optical communication used in the near infrared region of 1.3 to 1.5 m is a mixed crystal of silver chloride and silver bromide and Polarizing glass has been produced by stretching particles having a particle size of 50 nm or more. For this reason, the technique regarding the polarizing glass for visible regions by this invention is not disclosed at all.

[0030] In the present invention, not only the grain size of the silver grains but also the composition of the precipitated silver halide grains is scrutinized, and the silver chloride-free grains that do not contain bromine should transmit light having a transmittance around 500 nm. We have found that it is possible to increase the percentage and increase the extinction ratio.

In the projection type liquid crystal display device, a mercury lamp is used as the light source, and the visible light source often includes an ultraviolet light component. Glass with silver halide fine particles deposited has an absorption band that extends from the visible to the near-infrared when irradiated with ultraviolet light, and the glass is colored.When the ultraviolet light is blocked, the glass returns to its pre-irradiation state. And is widely known by the name of photochromic glass.

[0032] In the transmission spectrum (T || spectrum) of light with a polarization plane parallel to the longitudinal direction of metal fine particles with shape anisotropy in Figure 2, the wavelength range of 500 to 700 nm is good. Although absorption occurs, a transmission peak due to the inversion mode of surface plasmon resonance absorption is observed in the 300 to 400 nm wavelength region. Since this band light just corresponds to the photosensitive wavelength of silver halide, the silver halide remaining without being reduced inside the polarizing glass is exposed to light, and the transmittance in the visible region is lowered. Therefore, it is preferable to select a material that does not exhibit photoguchimism for the visible range polarizing glass of the present invention.

[0033] As prior art related to a polarizing glass that does not exhibit photo-irregularity, Cu O is hardly contained or the mother glass composition is limited (in molar ratio (R ₂ 0_A I ₂ 0 ₃ ): B ₂ 0 ₃ <0 25) technology (Patent Document 9), a technology that substantially does not contain CuO and adds an effective amount of C e 0 ₂ to keep silver in the glass in an oxidized state (Patent Document 10) and substantially free of C u O, K ₂ 0 and contains many and B a O was prevented reduction is limited to compositions strengthened basic pressure forte glass to metallic silver silver technique (Patent Document 1 1) [0034] In the present invention, an alkali oxide of 0.

By adding 5 to 5 wt% of nitrate, silver was dissolved as ions in the glass, and a non-photochromic glass could be obtained. That is, without the addition of C u O and C e 0 ₂ used as a silver oxidizing agent in a conventional technology, and, without limiting the composition of the base glass, could be obtained Nonfotoku port Mick glass.

The invention's effect

[0035] As described above, according to the present invention, there is provided a glass polarizer having a transmittance of 75% or more and an extinction ratio of 25 dB or more in the wavelength region from 500 nm to 600 nm. can do. The projection-type liquid crystal display device to which the glass polarizer having such performance and heat resistance and light resistance (particularly UV resistance) is applied enables the use of a light source with higher energy, and as a result, A small and brighter display device can be realized. Furthermore, the power of conventional resin polarizing films has been observed to deteriorate due to heat and light. By using polarizing glass with excellent heat resistance and light resistance, the image quality of the projection-type LCD can be maintained at a high level. . Brief Description of Drawings

[0036] FIG. 1 is a conceptual diagram of an optical engine of a liquid crystal projector (Patent Document 1).

FIG. 2 is a graph showing absorption spectra (Patent Document 4) of stretch-oriented silver particles and non-oriented silver particles.

[FIG. 3] FIG. 3 is a graph showing a transmittance curve (Patent Document 7) of light polarized by visible light by stretching of copper particles.

FIG. 4 is a graph showing a visible light polarized light transmittance curve (Patent Document 7) by stretching of silver particles.

FIG. 5 is a graph showing light transmittance and extinction ratio curves of Example 1 in the range of 4800 nm to 620 nm.

FIG. 6 is a graph showing light transmittance and extinction ratio curves of Example 2 in the wavelength range from 4800 nm to 620 nm. FIG. 7 is a graph showing light transmittance and extinction ratio curves in the wavelength range of 4 80 nm to 6 20 nm in Example 3.

FIG. 8 is a graph showing light transmittance and extinction ratio curves of Example 4 in the range of 4800 nm to 620 nm.

FIG. 9 is a graph showing light transmittance and extinction ratio curves of Example 5 in the wavelength range from 4800 nm to 620 nm.

FIG. 10 is a graph showing light transmittance and extinction ratio curves of Example 6 in the wavelength range of 4800 nm to 620 nm.

[FIG. 11] FIG. 11 is a graph showing the light transmittance and extinction ratio curve of Comparative Example 1 in the wavelength range of 4800 nm to 620 nm.

FIG. 12 is a graph showing light transmittance and extinction ratio curves in the wavelength range of 4 80 nm to 6 20 nm of Comparative Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. Manufacturing technology for carrying out the present invention is based on the technology for manufacturing known infrared polarizing glass, and technology for refining silver halide precipitated grains and technology for preventing the realization of photoguchimism are added. It is realized by doing.

[0038] First, a glass batch having a predetermined composition is prepared. At this time, pay attention to the following items and select the composition and raw materials. The glass applied to the polarizer used in the visible light region must be selected from glass that does not have so-called photochromic properties, whose transmittance deteriorates when irradiated with light. To this end, glass materials must be devised to strictly avoid copper oxide impurities. In addition, the composition of the amount of silver halide introduced is finally selected to be a value that can achieve both transmittance and extinction ratio.

[0039] A glass batch having a predetermined composition is melted and poured into a mold to produce a plate-like glass. Next, metal halide particles are deposited in the mother glass by heat treatment. In general, the lower the heat treatment temperature and the shorter the heat treatment time, the smaller the particle size. The heat treatment conditions are optimized depending on the glass type and composition. [0040] The mother glass in which metal halide particles having an average particle diameter of 40 nm or less are dispersed is subjected to a predetermined processing to become a plate-like preform and is transferred to a stretching process.

[0041] In the drawing process, the viscosity of the glass (directly the heating temperature), the drawing tension (the force for drawing the glass = so that the reduced metal particles have an appropriate aspect ratio) Adjust the load on the glass and stretch the preform.

[0042] The stretched glass is subjected to a reduction treatment so that part or all of the stretched silver halide grains become silver particles. The time and temperature of the reduction treatment and the atmosphere determine the depth of the reduced metal particle layer present near the surface and must be carefully determined to achieve the final properties. Thereafter, an antireflection film is formed to complete the polarizing element of the present invention.

Example

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Table 1 shows examples and comparative examples. The technical scope of the present invention is not limited to the following examples.

2,23 W w *; 尸 d; 尸 0044 / os 0580.08 B.30 A -o

_{9. 5%, L i 2 O} ;. 1 9%, N a 2 O; 2. 0%, K 2 O; 9. 6%, A g; 0. 3 2%, CI; 0. 3 7% S i 0 ₂ , H ₃ B0 ₃ , AI (OH) ₃ , L i ₂ C0 ₃ , N a N 0 ₃ , (N a ₂ C0 ₃ ), K ₂ C0 ₃ , N a CI, A raw material batch was prepared by blending A g CI as a raw material. At this time, 2% by weight of 3 ₂₀ was used as a nitrate raw material! \ 1 ₃ 1 \ 10 ₃ (sodium nitrate). This raw material batch was melted in a platinum crucible with a capacity of 3 OO cc at 1 430 ° C for 4 hours, then poured into a mold and pressed with a roller, approximately 250 x 60 x 2.5 mm thick sheet glass Got.

[0045] This plate glass was heat-treated to precipitate silver chloride particles. The grain size of silver chloride grains was controlled by the heat treatment temperature and heat treatment time shown in Table 1. Table 1 also shows the results of measuring the average particle size of silver chloride grains using an electron microscope.

[0046] The obtained glass preform is set vertically in a stretching furnace, and the preform is fed at a constant speed and the stretching is performed while the preform feeding speed and the take-up speed are balanced, and stretching is performed. It was. Table 1 shows the viscosity and stretching tension of the glass during stretching (load per unit area on the glass). The stretching tension was controlled mainly by the glass heating temperature. (These speed settings are also shown in Table 1.)

[0047] After the stretched glass tape was cut to about 5 Omm length and polished on both sides, the reduction conditions shown in Table 1 were performed while flowing hydrogen gas at a rate of about 1.5 liters / minute in a reducing furnace. Temperature and time).

[0048] Next, in the film formation process, after washing and drying, a plurality of samples are set in the vapor deposition chamber, and four alternating layers of Si 0 ₂ and Ta ₂ 0 ₅ (antireflection film) Was deposited on both sides of the sample by sputtering or vacuum deposition to provide an antireflection effect.

[0049] Table 1 shows the polarization characteristics of the polarizing glass thus produced. Also, the examples "! ~ 6 and comparative examples"! The transmittance spectrum (T 丄%) of light having a polarization plane perpendicular to the longitudinal direction of the metallic silver particles in the wavelength range of 500 nm to 600 nm (actually 480 nm to 62 O nm) of Figures 5 to 10 and Figures 11 and 12 show the extinction ratio data in the wavelength range.

[0050] The extinction ratio is 500 η in the transmission spectrum measured using a spectrophotometer. The average transmittance of light having a polarization plane perpendicular to the longitudinal direction of the metallic silver particles in the wavelength region of m to 600 nm, and the average transmittance of light whose polarization plane is parallel to the longitudinal direction of the metallic silver particles T || Calculated from% by the following formula. Table 1 shows the minimum extinction ratio in the wavelength region of 500 nm to 600 nm.

Extinction ratio (d B) = 1 0 XI og ₁₀ (T 丄% / T II%)

[0051] As is clear from Table 1, when the glass composition is the same, the lower the heat treatment temperature, the smaller the average grain size of silver chloride precipitated. The average transmission of light having a polarization plane perpendicular to the longitudinal direction of the metallic silver particles in the wavelength region of 500 nm to 600 nm under the condition that the average particle diameter is 40 nm or less (Examples “! To 6”). A polarization characteristic was obtained in which the ratio (single% ₅₀₀ to _{600 nm} ) was 75 <½ or more and the minimum extinction ratio in the wavelength range was 25 dB or more.

[0052] In Comparative Examples 1 and 2 where the average particle diameter exceeds 40 nm, as shown in Table 1, both the T 丄 transmission spectrum and the extinction ratio are on the longer wavelength side even at a relatively low stretching tension. Even if the stretching and reduction conditions are changed to shift, the average transmittance of 75% or more (T _nm % ₅₀₀ to _{600 nm} ) and the minimum of 25 dB or more in the wavelength range of ₅₀₀ _nm to ₆₀₀ ηm The extinction ratio could not be obtained at the same time.

[0053] [Comparative Example 3]

CI in glass composition: 0.1% and 0.2% of 0.3% by weight of glass were dissolved with equimolar amounts of Br: 0.23% and 0.45%, and then halogenated. Polarized glass was prepared using the same method and conditions as in Example 1 for glass preforms that had been heat-treated so that the average particle diameter of silver particles was 18 nm, which was the same as in Example 1, and the polarization characteristics were compared. As a result, both the spectra of the light of the polarization plane perpendicular to the major axis and minor axis direction of the metallic silver particles are shifted to the longer wavelength as the amount of Br increases, and at 500-60 Onm. The average transmittance and minimum extinction ratio decreased from 82% and 25 dB of Example 1 with CI only to 76%, 25 dB, 68%, and 8 dB, respectively.

[0054] Next, the glass polarizers obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were irradiated with a 500 W xenon lamp at a distance of 40 cm for 15 minutes. The change in transmittance was visually observed and the change in transmittance at 650 nm before and after irradiation was measured to determine the presence or absence of photochromic properties. As a result, in any of the polarizers obtained in Examples 1 to 6 and Comparative Examples 1 and 2, no change was observed before and after irradiation, and it was confirmed that no photochromic characteristics were exhibited. This means that the glass polarizer according to the present invention does not cause deterioration of polarization characteristics or transmittance characteristics even when irradiated with light of ultraviolet and visible short wavelengths.

[0055] [Comparative Example 4]

0. 2% by weight of Na ₂ O was introduced from the nitrate raw material Na NO ₃ (sodium nitrate), and was obtained by melting a raw material batch prepared without using any other nitrate raw materials In the glass polarizer produced from the glass of the same composition under the same conditions, the photochromic characteristics were clearly observed with the irradiation of the xenon lamp. It is probable that the unreduced silver chloride particles inside the glass polarizer were exposed to light, causing a decrease in transmittance at 650 nm.

[0056] As explained above, by controlling the average particle size of silver chloride deposited and dispersed in the mother glass to 40 nm or less depending on the heat treatment conditions, it is good in the green wavelength region of 500 nm to 600 nm. Polarization characteristics, that is, an average transmittance of 75% or more (choice% ₅₀₀ to _{600 nm} ) and an extinction ratio of 25 dB or more were achieved.

[0057] In addition, the glass component is substantially free of a copper compound, and a glass raw material corresponding to 0.5 to 5 wt% of the glass oxide composition is introduced with nitrate to melt. Thus, it was possible to obtain a polarizer that does not exhibit photochromic characteristics, that is, does not cause deterioration of polarization characteristics or transmittance characteristics even when irradiated with light of ultraviolet and visible short wavelengths.

[0058] As described above, according to the present invention, in the green wavelength region from ₅₀₀ _nm to _{600 nm} , an excellent transmittance having an average transmittance of 75% or more (Tl% ₅₀₀ to _{600 nm} ) and an extinction ratio of 25 dB or more is obtained. A polarizer can be provided. This can be used for a liquid crystal display device such as a liquid crystal projector with sufficient performance. Also follow Considering that conventional polarizers are used by attaching a resin-made polarizing film that is sensitive to heat and ultraviolet rays to sapphire, quartz glass, or glass substrates, the mother glass has high heat resistance and thermal shock resistance. By replacing the glass polarizer according to the present invention, which is a borosilicate glass, the optical engine of the projector itself can be simplified, for example, cooling measures including the installation of a cooling fan can be reduced or unnecessary. Conceivable. Furthermore, the glass polarizer according to the present invention does not exhibit photochromic characteristics, and other performance is hardly deteriorated, so that the image quality of the liquid crystal projector is maintained high, and as a result, the life of the liquid crystal projector itself is extended. Be expected.

Claims

The scope of the claims

[1] After heat-stretching borosilicate glass in which silver halide grains are dispersed and precipitated by heat treatment, at least a portion of the silver halide grains oriented and elongated in the glass is reduced to produce metal silver grains. The wavelength range of 500 nm to 600 nm of light having a plane of polarization perpendicular to the longitudinal direction of metallic silver particles having shape anisotropy dispersed in a uniaxial orientation. average transmission (T丄^{_{0/0 5 0 0~6 0 0}} nm) is not less 7 5% or more, and an extinction ratio in the wavelength region is a visible light, characterized in that it is 2 5 d B above Glass polarizer.

[2] The glass polarizer for visible light according to [1], wherein the silver halide grains dispersed and precipitated in the glass by heat treatment have an average particle size of 40 nm or less.

[3] The glass polarizer for visible light according to [1] or [2], wherein the silver halide grains dispersed and precipitated in the glass by heat treatment are silver chloride grains.

[4] The borosilicate glass does not substantially contain a copper compound as a glass component, and a glass raw material corresponding to 0.5 to 5 wt% of the glass oxide composition is introduced with nitrate to melt. 4. The glass polarizer for visible light according to claim 1, 2 or 3, wherein the glass polarizer is an all-force real minoborosilicate glass that does not exhibit photochromic properties.